Error map construction and compensation of a NC lathe under thermal and load effects

Thermally induced errors and load-induced errors are two key factors affecting the accuracy of machine tools. This paper proposes a strategy to build an error map of a machine tool by considering both thermal and load effects. A moderation model is developed to analyze the positioning errors with thermal effects, and a Fourier series model is used to fit the straightness errors. Based on actual cutting tests, relationships between cutting forces and motor currents are established. A load test is conducted in which a pushing cylinder is used to simulate actual cutting forces. The changes in error motions under different loads are obtained. An experimental verification is conducted on an NC lathe, whose error map is generated by integrating thermal and load effects. As actual cutting results show, when thermal and load effects are simultaneously compensated, the machining accuracy increases by 10 % as compared with when only thermal effects are compensated.